Japanese patent application published on 29 Sep. 2005 under the No JP 2005-264086 describes blends of polystyrene (PS) and PLA in which PLA is the major part.
Japanese patent application published on 18 Jan. 2000 under the No JP 2000-017038 describes an expandable resin having biodegradability. This composition is made essentially of PLA and comprises 25% or less by weight of PS.
U.S. Pat. No. 7,160,948 in example 1 describes a composition as follows: 26.3% by weight of polylactic acid, 26.3% by weight of polymethyl methacrylate, 11.6% by weight of polyolefin and 35.8% by weight of a block copolymer of methyl methacrylate and styrene, said block copolymer comprising 30% of PS. This means clearly that the polystyrene is not the major part of the composition.
Japanese patent application published on 8 Dec. 2005 under the No JP 2005-336666 describes lactic acid fibers containing by weight 3 to 15% of syndiotactic polystyrene.
WO 92-04413 describes blends of PLA and general purpose polystyrene comprising by weight 10 to 25% of PLA. These blends are made by compounding PLA and PS, no structure is described. Because there is no compatibilizer and/or no functionalization of the PLA the PLA is not finely dispersed in the PS matrix and thus mechanical properties are poor.
It has now been discovered monovinylaromatic polymer compositions comprising a finely dispersed phase of at least one polymer made from renewable resources. Said polymer made from renewable resources can be selected from poly(α-hydroxyacids) and polyhydroxyalkanoates. Among these latters, polylactic acid (PLA), poly-3-hydroxybutyrate (P3HB), polyhydroxyvalerate (PHV), polyhydroxyhexanoate (PHH), polyhydroxyoctanoate (PHO) and their copolymers are mostly preferred. Most preferably, PLA is used as the bio-sourced dispersed polymer phase. Said compositions can be made as follows:
by blending functionalized bio-sourced polymers, or mixtures of bio-sourced polymers and functionalized bio-sourced polymers, with monovinylaromatic polymer; or
by polymerizing monovinylaromatic monomer in the presence of functionnalized bio-sourced polymers, or mixtures of bio-sourced polymers and functionnalized bio-sourced polymers; or
by polymerizing monovinylaromatic monomer in the presence of bio-sourced polymers and at conditions effective to generate a compatibilizer of bio-sourced polymers and monovinylaromatic polymer.
Optionally these compositions comprise a rubber.